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The lack of highly efficient blue‐emitting perovskite nanocrystals limits their development for optoelectronic applications. In article number 2001698, Bartomeu Monserrat, Shuyu Zhang, and co‐workers develop blue‐emitting neodymium‐doped CsPbBr3 nanocrystals with high photoluminescence quantum yield (PLQY) and narrow spectral width. First principles calculations reveal the microscopic mechanisms for the blueshift of photoluminescence and the enhancement of PLQY upon doping. [Image: see text]

Colloidal CsPbX3 (X = Br, Cl, and I) perovskite nanocrystals exhibit tunable bandgaps over the entire visible spectrum and high photoluminescence quantum yields in the green and red regions. However, the lack of highly efficient blue‐emitting perovskite nanocrystals limits their development for optoelectronic applications. Herein, neodymium (III) (Nd3+) doped CsPbBr3 nanocrystals are prepared through the ligand‐assisted reprecipitation method at room temperature with tunable photoemission from green to deep blue. A blue‐emitting nanocrystal with a central wavelength at 459 nm, an exceptionally high photoluminescence quantum yield of 90%, and a spectral width of 19 nm is achieved. First principles calculations reveal that the increase in photoluminescence quantum yield upon doping is driven by an enhancement of the exciton binding energy due to increased electron and hole effective masses and an increase in oscillator strength due to shortening of the PbBr bond. Putting these results together, an all‐perovskite white light‐emitting diode is successfully fabricated, demonstrating that B‐site composition engineering is a reliable strategy to further exploit the perovskite family for wider optoelectronic applications.

Visible light communication (VLC) is becoming an important and promising supplement to the existing Wi-Fi network for the coming 5G communications. Organic light-emitting semiconductors present much fast fluorescent decay rates compared to those of conventional colour-converting phosphors, therefore capable of achieving much higher bandwidths. Here we explore how nanopatterned organic semiconductors can further enhance the data rates of VLC links by improving bandwidths and signal-to-noise ratios (SNRs) and by supporting spatial multiplexing. We first demonstrate a colour-converting VLC system based on nanopatterned hyperbolic metamaterials (HMM), the bandwidth of which is enhanced by 50%. With regard to enhancing SNRs, we achieve a tripling of optical gain by integrating a nanopatterned luminescent concentrator to a signal receiver. In addition, we demonstrate highly directional fluorescent VLC antennas based on nanoimprinted polymer films, paving the way to achieving parallel VLC communications via spatialmultiplexing. These results indicate nanopatterned organic semiconductors provide a promising route to high speed VLC links.

Visible light communication (VLC) is a promising candidate for high-speed wireless communication with numerous unlicensed spectrum. To achieve high-speed data communication, it requires intense light signals concentrated on a tiny fast photodiode. The common way of using focusing optics reduces the field of view (FoV) of the photodiode due to the conservation of etendue. Luminescent solar concentrators (LSC) provide a solution to enhance the signals without affecting the FoV. In this paper we demonstrate nanopatterned LSCs fabricated on flexible plastics that achieve a doubling of optical gain compared to its traditional rectangular counterparts. These LSCs can free VLC detectors from complex active pointing and tracking systems, making them compatible with smart mobile terminals in a simple fashion.

Organic light-emitting semiconductors present much shorter lifetimes compared to conventional phosphor colour converters, therefore capable of achieving much higher bandwidths in visible light communications. This talk focuses on addressing two of the coming challenges for organic semiconductors: spatial multiplexing and bandwidth enhancement, and explores the roles of photonic nanostructures as a solution to both challenges. The appealing features of visible light communications (VLC), including fast speed, numerous unregulated bandwidth and high security, make VLC an important and promising supplement to the existing Wi-Fi network for the coming 5G communications [1-4]. So far most of the fast VLC links are based on micro-LEDs or laser diodes (LD) which have bandwidths at GHz level, however, in order to achieve high-quality white light, a practical and simple way is to combine a colour converter with the fast-modulated blue LED/LD backlight. Conventional phosphors have bandwidths of only several MHz, so the overall bandwidths of white light sources are severely limited. Organic light-emitting semiconductors have demonstrated intriguing capabilities of boosting bandwidths due to their nanosecond-scale lifetimes [5-10]. For example, conjugated polymers demonstrate bandwidths of over 200 MHz, which are enhanced by two orders of magnitude compared to those of conventional phosphors. This talk focuses on addressing two of the coming challenges for organic semiconductors: i) Can organic semiconductors be applied for parallel communications like multiple-in-multiple-out (MIMO)? ii) Are there potential solutions to further improve the bandwidths of organic semiconductors if the molecular design of fast organic emitters has reached its bottleneck? Colour tuning for organic semiconductors is facile, so parallel communications based on wavelength division multiplexing can be easily realised. On the contrary, organic semiconductors are not born for spatial multiplexing, since they are generally Lambertian emitters. Our strategy to overcome this problem is to use photonic.

Room temperature recrystallization is an intriguing method of fabricating CsPbX3 perovskite quantum dots since it does not involve high temperature or inert atmosphere, offering a promising route to the mass production of CsPbX3 quantum dots at low cost. However, their performance stability during work was seldom investigated and was far from the requirements for practical applications. Here, we demonstrate a facile and low-cost method to significantly improve the thermal, photo- and water stability of room-temperature synthesized perovskite quantum dots by effectively suppressing the unfavored grain growth and surface trap states. The fabricated quantum dots of green-emitting CsPbBr3 and red-emitting CsPbBr1.2I1.8 were applied for quantum dot-converted white LEDs, which are capable of achieving a wide color gamut of 135% NTSC and 101% Rec. 2020.

This paper analyzes and studies of a threshold group signature scheme which is based on ElGamal type. In order to overcome the shortcomings of the scheme, a new threshold group signature scheme with privilege subjects based on ECC is proposed. The new scheme is able to prevent the fraud of key distribution center effectively. Only when the scheme satisfies (t, n) and (t1, n1) threshold signature, can the valid signature be generated. Thus the scheme reached the property of threshold. The program also satisfies the properties of anonymity, unforgeability, trace ability, reversibility and it can resist collusion attacks too.